This also cleans up some weird potentially-buggy logic paths within the
ModifierKeycode creation and handling. I can now press a free-floating
HYPER in my keymap and see the appropriate codes in `xev` for press and
release events.
Quote taken straight from the docstring of get_pin:
>Cross-platform method to find a pin by string.
>
>The pin definitions are platform-dependent, but this provides
>a way to say "I'm using pin D20" without rolling a D20 and
>having to actually learn MicroPython/CircuitPython and the
>differences in how they handle pinouts.
>
>This also makes the keymap sanity checker actually work for
>CircuitPython boards, since it's not possible in CPY to
>define a module stub for `board` that uses Passthrough
>natively (which is how the MicroPython stub worked originally)
